Rev. Roum. Sci. Techn.– Électrotechn. et Énerg., 54, 1, p. 29–36, Bucarest, 2009 STRIPS METHOD FOR EVALUATING A.C. LOSSES IN SLOT PORTION OF ROEBEL BARS – ERRORS ANALYSIS TOMA DORDEA 1 , AUREL CÂMPEANU 2 , GHEORGHE MADESCU 1 , ILEANA TORAC 1 , MARŢIAN MOŢ 1 , LUCIAN OCOLIŞAN 1 Keywords: High power synchronous machines, Roebel bar windings, Optimization. This work deals with the additional losses minimization in the Roebel bar windings of high power synchronous generators. In order to solve this problem, in the paper is presented a strips-method that provides a high accuracy estimation of the elementary currents through the strand conductors. According to this method, the cross section of each strand in N parallel-strips with the slot basis was divided, so that the strip-current density could be considered as a constant. The aim of the paper is to analyze the computing-method errors and the influence of the strips number on these errors. 1. INTRODUCTION Stator windings in large hydrogenerators use Roebel bars in which the strands (elementary conductors) are complete transposed in the slot portion by a variety of arrangements. In a normal bar, that have a 2π transposition, each strand has two crossovers, and, after passing through the slot portion, is in the same position relative to the other strands. Thus, each strand has the same mean depth in the slot, the same leakage reactance and the same voltage induced by the both main and leakage fluxes. However, in the endregions of the generator, leakage flux flowing through the bars produces voltage differences between the strands. Currents circulate between the strands in addition to the normal load current, and additional losses results. Minimization of these additional losses is an important objective having as effect the increase of the efficiency of high power synchronous generator. The Roebel bar optimization problem supposes to find the number of the strands and the transposition angle in the slot portion; so that the bar loses have the minimum value. 1 Romanian Academy, Timişoara Branch, E-mail: tdordea@d109lin.upt.ro 2 University of Craiova, Faculty of Electromechanics, E-mail: acampeanu@em.ucv.ro